Antonyms for "un-exciting" would be words that describe something that is interesting, stimulating, or captivating. Some examples include thrilling, exhilarating, exciting, invigorating, and fascinating. Other antonyms for un-exciting could be words that describe something as lively, energetic, or dynamic, such as vibrant, animated, dynamic, or lively. Additionally, words that suggest something that is impressive or awe-inspiring can also be considered antonyms for un-exciting, like impressive, remarkable, extraordinary, or awe-inspiring. In essence, any word that denotes a feeling of excitement, passion, wonder, or delight can be used as an antonym for un-exciting.